Ship propulsion control



ug- 24, 1948. A E. FRiscH ErAl.- 2,447,643

SHIP PROPULS ION CONTROLS Filed Jan. 25, 194'? 5 Sheets-Sheet l l@ 6" s l s a www GZ faz GQFQFCS f ATTORNEY Aug. 24, 1948.

E. FRISCH ET Al.

SHIP PROPULSION CONTROLS Filed Jan. 23, 1947 L g ygg SW/ Tal/5 P0 SlT/0N Afa /n/ alza/.1,4m .wf

FUN O O O O O START Ol O O O aff- O Lil/ER WITNESSES 20 swzrch'fs 3 Sheets-Sheet 2 ATTORNEY Aug. 24, 1948. E. FRlscl-l ET Al.

SHIP PROPULSION CONTROLS 3 Shee'ts-Sheet 5 Filed Jan. 23, 1947 INVENTORS E'zizzzy 'zz'c and B47027022@ Lory. PM2 i.

' ATTORNEY Patented Aug. 24,V 1948 SHIP PROPULSION CONTROL Erling Frisch, Pittsburgh, and Marion R. Lory, Irwin, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 23, 1947, Serial No. 723,760

(Cl. 318i-178) 21 Claims. 1

This is a continuation of our copending patent application Serial No. 496,730, filed July 30, 1943, and abandoned after the filing of this continuation.

Our invention relates to systems for controlling alternating-current drive motors energized from prime-mover alternator sets, and especially to a. control system of this type for Diesel-electric ship propulsion.

The prime movers, such as Diesel engines, of the drive systems here in point are equipped with a speed governor which controls a supply valve or the like fuel control member inl order to maintain the speed of the engine and hence the frequency of the alternator voltage and the speed of the drive or propulsion motor approximately at a datum value which is varied by the operator for changing the engine and motor speeds accordingly. v

While the known drive systems of this kind afford a satisfactory operation and speed control under steady operating conditions, the prime movers show the tendency to stall during reversal periods and also when starting the motor with a reduced number of engine-alternator sets in operation.

It is a basic object of our invention to improve motor control systems of the class indicated so as to eliminate or greatly reduce the tendency of the prime movers to stall under unsteady operating conditions. More particularly, the invention aims at improving in this manner the Dieselelectric drives of ship propulsion systems provided with synchronous or induction motors.

Another object in line with the foregoing is to improve the starting conditions of such motor control systems so as to reduce the skill and attention heretofore required from the attendants for starting or reversing the drive without noticeable stalling. A related object of the invention is to improve the motor control and hence in the case of ship propulsion systems, the maneuverability of the vessel provided with such a system by reducing the stalling tendency when starting or reversing the propulsion motor.

According to one of the considerations involved in this invention, one of the component causes for the stalling of the prime mover in the known systems is the fact that, when the alternators are connected to the bus and synchronized before starting the propulsion motor, there will' be a sudden inrush of power to the motor as soon as the latter is connected to the bus. The resulting sudden load on the engines will cause them to slow down until the speed governors take hold and readjust the fuel supply control to a more fully open position. Due tov the low inertia of the engines and alternators as compared with the inherent delay of the governor action, the engines may slow down to below the minimum stable speed and will stall before the fuel control is properly adjusted. Accordingly, a more specific object of our invention is to prevent the sudden application of power to the drive motor and thereby to the engines, and to obtain a more gradual energy transmission and acceleration with the effect of reducing the disturbing reaction just explained.

Another component cause of the stalling tendency, also considered by this invention, relates to the fact that the torque which can be developed by the engines at low speeds, such as are required for maneuvering a vessel, is lower than their full speed torque and is not necessarily suf-- oient to meet the torque requirements of the connected alternators during the low speed or maneuvering periods. The alternator torque is determined by the starting torque of the motor plus the losses of the motor and alternators. The starting torque is a function of the electrical characteristics of the motor and alternators and has no relation to the actual torque requirements of the element, such as the ship propeller, to be driven. The difference between the starting, torque and the propeller torque, for instance, represents the torque actually available for aoceleration. Having these torque conditions in mind, we also aim by this invention to control. in periods of acceleration the alternator torque relative to that oi the engines so that it is substantially matched by the engine torque, thereby preventing essentially the just-mentioned other component cause of the stalling tendency.

A still further object, allied to the one last referred to, is to provide a control system as set forth above in which the field energization of the alternators is so regulated that the alternator torque, in periods of acceleration, is always at or near the maximum which can be developed by the engines without pulling the speed down below a permissible minimum value.

These and other objects, as well as the means provided by the invention for achieving the stated aims and advantages, will be apparent from the following description of the embodiment shown in the drawings in which:

Figure 1 shows a straight-line diagram of a system of control for operating the synchronous motor of a Diesel-electric ship propulsion plant;

Fig. 2 is a sequence chart of the contacts for connecting one of the alternators of the same system to the propulsion bus;

Fig. 3 is a sequence chart of the contactors appertaining to the switch mechanism for starting and reversing the propulsion motor, also referring to the system of Fig. 1;

Fig. 4 Yis a plan view on an embodiment of a control board applicable in the system of Fig. 1 for operating the switch and contact means referred to in Figs. 2 and 3;

Fig. 5 is explanatory and shows a torque-speed diagram of a prime mover and the propulsion motor of the same system; and

Fig. 6 illustrates the same system as .shown in Fig. 1 but with a substantially complete diagrammatic showing of contact apparatus for controlling the switches and other contactors indicated in Fig. 1 in the necessary sequence and cooperation apparent from the sequence charts of Figs. 2 and 3.

Referring to Fig. 1, the Diesel-electric ship propulsion system illustrated therein comprises a synchronous propulsion motor MOT for driving the ship propeller PRO. The propulsion motor is connected to a propulsion bus PB which is `fed from one or several of a group of alternators of which three are exemplied in the illustration and denoted by ALI, AL2 and AL3. `Each alternator is driven by a Diesel engine DEI, DEZ, or DE3. The fuel supply system of each engine, here schematically represented by a fuel supply conduit FSI, FS2 or FSB is provided with a fuel or charge control device FCI, FCZ, and FC3, respectively. Each fuel control device is governed by a speed governor SGI, SGZ and SG3, respectively. The governors are connected with a common master speed control MSC in order to maintain the simultaneously operating Diesel engines at approximately the same speed. The datum value of this speed is adjustable by means of a speed control lever SCL. The connection between the master control and the individual controls, here schematically indicated by a broken line connection, may be of hydraulic, electric, or mechanic type, and the speed governors and master control may be of any kind available for such purposes. Details of the Diesel-electric drive and the appertaining speed control are not shown in the drawing because various methods and construction of such a control are well known in the art and do not form an essential part of the invention proper.

'It will appear from the general survey just given that the operating speed of the synchronous motor MOT depends on the speed of the alternators and hence on the speed of the Diesel engines set by the speed control lever SCL. In order to vary the motor and propulsion speed, the speed control lever SCL is displaced accordingly.

Turning now for a moment to Fig. 4, the speed control lever SCL will be seen in the latter illustration as regards its arrangement on the control stand relative to four other control Alevers MCL, CLI, CL2 and CL3. Lever CLI serves to connect the alternator ALI (Fig. 1) to the propulsion bus PB and also to control the field excitation of this alternator. Accordingly, levers CL2 and CL3 serve to control the bus connection and eld excitation of the alternators AL2 and AL3, respectively. By placing any of levers CLI, CL2 and CL3 from the off position into the start and subsequent run position, any of the three alternators and any combination thereof may be rendered eiective to feed alternating current to the propulsion bus PB, the connected and field-excited alternators running in approximate synchronism due to the function of the master speed control. The lever MCL serves to control the starting and reversing operation of the propulsion motor MOT.

In order to effect the just-mentioned control operations of :levers MCL, CLI, CL2 yand CL3 in accordance with the above-stated objects of the invention, a number of cooperative circuit elements and contactors are provided whose design, arrangement and operation will now be described while reverting to Fig. 1 of the drawings.

The alternator ALI has its armature AAI connected with the ,shaft of the Diesel engine DEI. The youtput circuit of the armature is connected with the propulsion bus PB by three switches denoted 7by Ail-0, A'II and AIZ. The field Winding AFI oi alternator ALI is connected by switches A`I3 and AI4 to an exciter bus EB fed with direct current from an exciter generator AG to be described more in detail in a later place. A resistor RI is connected in parallel to field winding AFI, 4the parallel connection being controlled by a switch AI5.

Similarly, the armature AA2 of alternator AL2 is lelectrically connected to the propulsion bus PB by switches A20, A2I and A22, while the vappertaining fiel-d winding AF2 is connected to the exciter bus EB by switches A23 and A24. A resistor R2 is arranged in shunt connection to eld winding AF2 over a control switch A25.

Again, similar t-o the circuit connections of the just-mentioned alternator, the alternator AL3 has its armature AA3 connected to the propulsion bus PB through switches A30, A3I and A32 and its eld winding AFB connected through switches A33 and A34 with the exciter bus EB, a resistor R3 controlled by a switch A35 being connected in parallel to the eld winding AF3.

vWhile we have illustrated in Fig. 1 a number of separate switches denoted by AI 0 through A15, A20 through A25, and A30 through A35, it will be understood from Fig. 6 that each of these three groups of switches belongs to three sequentially operating contact apparatus which are controlled by the above-mentioned control levers CL1, CL2 and CL3, respectively. The other switches or contact means shown in Fig. 1 and to be described presently are also associated with one another and form a fourth contact apparatus so as to be operated in a given cooperative and sequential relation to one another. This fourth contact apparatus, as will appear from Fig. 6, ls provided with the above-mentioned control lever MCL (Fig. 4)

According to Fig. 1, the Yarmature MA of the propulsion motor MOT is connected through a group of reversing switches SI through S6 with the propulsion bus PB. Only one of switch groups SI, S2, S3, or S4, S5, S6 is closed at a time so that the motor runs in one or the other direction. Three resistors RII, R5 and R6 are connected through switches S'I, S8 vand S9 to the in-leads of the armature MA. These resistors serve for the vdynamic braking of the motor when reversing the direction of propulsion. Hence the switches S'I, S8 and S9 are closed and opened in an appropriate sequence to the operation of the other motor control switches of the system as will also be explained later when referring to Fig. 6.

The eld winding MF of the propulsion motor MOT is connected through switches SIO and SI I to a direct-current exciter circuit EC fed from an exciter generator MG (Fig. 1). A resistor RI is arranged in shunt to the motor eld winding MF. The shunt connection is controlled by a switch SI2. Also in parallel to the mot-or field winding MF is connected another resistor R8, the connection being controlled by a switch SM. Another switch, SI3, lies in a short-circuiting path to resistor R8 and switch SI4. The exciter bus EB serving to energize the alternator field windings AFI, AF2 and AFB, and the exciter circuit for energizing the motor field winding MF have a common lead which contains an interrupting switch SI5.

The above-mentioned exciter generators AG and MG form part of an exciter set EXC. The armatures AGA and MGA of the two generators are mounted on a common shaft ES which is driven by a constant speed motor CSM. Due to the constant speed of rotation of the two armatures AGA and MGA, the voltage of the exciter bus EB and the voltage of the exciter circuit EC are dependent upon the respective energization of the eld windings AGF and MGF. These eld windings are connected to a constant voltage bus CVB fed from a suitable direct-current source CVS. The mid-point between windings AGF and MGF is directly connected with one of the leads of the constant voltage bus CV'B. The other terminal of field winding MGF is connected through a resistor R9 and an adjustable rheostat RID with the other lead of bus CV'B. The other terminal of field winding AGF is similarly connected through a resistor RII and an adjustable rheostat RI2 with the last-mentioned lead of bus CVB. However, another variable resistance or impedance member RI3 is interposed between resistors RII and RIZ in order to effect an automatic voltage control. The resistors RI 2 and RI 3 are shunt-connected to respective switches SI'I and SIE. appertaining resistor RI2 or RI3 is bridged and ineilective as far as the control of eld winding AGF is concerned.

The just-mentioned resistor or impedance member RI3 forms part of a voltage regulator VRG. The resistance member RI3 is tapped, and the taps are controlled by a movable member MM which, in turn, is actuated by a control coil CL. When the control coil is energized in an increasing degree, the movable member MM is so op- ""1 erated as to reduce the elective resistance of resistance member RI3.

The regulator unit VRG may consist of a s0- called Silverstat as described in U. S. Patent No. 2,249,826 issued July 22, 1941, to C. R. Hanna. However, any other type of regulator designed and operating in accordance with the requirements of this specification may be used instead.

The control coil CL of voltage regulator VRG is energized from the generator GA of a pilot regulator set PRSI which contains a pilot motor PM in mechanical driving connection with the armature GA of a pilot generator PG. The eld winding GF of the pilot generator PG is energized from the constant voltage bus CVB over an adjusting or Calibrating rheostat RI4. The pilot motor PM is of the induction type and is connected through switches SI9, S20 and S2I with the secondary SE of a step-down transformer TR whose primary PR is connected to the propulsion bus PB. Due to this connection, the pilot motor PM, when switches SIS, S20 and S2I are closed, runs in accordance with the frequency of the alternating current in the propulsion bus, and hence at a speed proportional to the speed of the Hence, if either switch is closed the alternators ALI, AL2 and AL3 and their respective engines DEI, DEZ and DES as controlled and set by the master speed control MSC (Fig. 4) and its control lever SCL. The adjustment of the field resistor RIII is not changed during the control operation once a proper calibration has been effected. Consequently, the excitation of the field winding GF remains constant during the operation of the system. As a result, the output voltage of the armature GA varies in accordance with the frequency and speed of the alternators ALI, AL2 and ALS so that the effective resistance or impedance of control element RI3 is changed automatically in dependence upon the speed of the alternators and engines.

The switch SIB is so operated, as will be explained subsequently, that the resistance member RI3 is inserted when the starting lever MCL is set for initial starting, and is decreased gradually by the action of control coil CL until the entire resistance of RIS is eiective in the field circuit of AGF if the engine speed is below a certain minimum at which the engine should run. As more resistance is inserted in this manner into the eld circuit of the exciter generator AG, the excitation supplied by exciter bus EB to the main generator eld windings AFI, AF2 and AFS will be reduced accordingly. As a result the torque imposed on the engine will decrease and the speed will be maintained at the desired minimum value. As the propeller speed decreases due to the slowing down of the forward motion of the vessel, the propeller torque will drop off and the engines will speed up causing a gradual increase in the exciter field current as a result of the regulating action of pilot set PRS and voltage regulator VRG. When the motor approaches synchronizing speed, the starting lever MCL will be advanced to the start 2 position and the regulator resistance RIS will be shorted out by switch SIB and the excitation of field winding AFI, AF2 and AF3 will become normal again. At this point the motor field MF is energized as will be explained presently.

As the voltage regulator is no longer required after the motor is synchronized, the pilot regulator PRS is disconnected by opening the switches SIS, S29 and S2! when moving the starting lever MCL to the +4 position after the closure of switch SIB.

By virtue of the just-mentioned feature of the invention, the acceleration of the motor when starting or reversing its operation is speeded up to virtually the highest extent possible with the engine torque then available.

The function and cooperation of the abovementioned elements of the control system will be more fully understood from the following summarizing description of the proper operating sequence of the various switch members. The proper sequence of the generator control contacts AIO through AI5 actuated by lever CLI will be understood from the sequence chart shown in Fig. 2. The corresponding sequential operation of switches A20 through A25 appertaining to lever CL2 and the sequential operation of switches A30 through A35 appertaining to control lever CL3 will also be understood from Fig. 2 since these switch groups are operated in analogy to the operation apparent from Fig. 2. The c0ac tion and sequential operation of the switches denoted by SI through S2! and serving mainly for controlling the starting and reversing operation of the propulsion motor is apparent from the sequence chart shown in Fig. 3.

Assuming the control levers SCL, MCL, CLI, CL2, and CL3 in the inactive positionsr illustrated' in Fig. 4, the operation of the propulsion drive is started as follows: At first the control lever of the alternator or alternators to be operated are placed from the 01T position to the start position and then in to the run position. For instance, if alternator ALI is to be operated, the control lever CLI is moved upwardly from on to start In the oli position according to Fig. 2, switches AIS through AIA are open and switch AI is closed. lt will be seen from Fig. l in this position the eld winding AFI of the alternator is shunted by resistor Ri. By moving lever CLI to start switches AIA, AI'I and AltI are closed and connect the armature AA! of the alternator to the propulsion bus. When now the alternator runs at datum speed, its eld winding AFI is still shunted, and since switches SIS, SIf and SI5 are all open in the stop position of lever MCL according to 3, the alternator field is not excited so that the machine runs idle. Now the lever CLI is moved from start" to run with the effect of opening switch AIE and closing switches AI 3 and AIi in addition to the previously closed switches Aie, AI! and AIE (see Fig. 2). The effect of this last control step is to disconnect resistor RI from the field winding AFI and to connect the terminals of the winding by switches Ai and Alli to exciter bus EB. However, since switches SI 3, SIG' and SI5 are still open in the stop position of lever MCL (Fig. 3), the eld winding AFI is now merely prepared for energization but is as yet not supplied with energizing voltage from exciter generator AG. The motor MOT is now in position to be started.

Referring now to the sequence chart of Fig. 3 in conjunction with the diagram of Fig. l, the starting operation of the propulsion motor will be described in detail.

When the motor is stopped, only switch Si? of the motor control system proper is closed (see Fig. 3). The eiect of this closure is to discharge and shunt the field winding MF of the propulsion motor through the resistor R'I. All other switches denoted by a reference character beginning with the letter S are open in the stop position of MCL. If the motor is to be operated for propulsion ahead, the lever MCL is moved the upward direction into the position denoted by +I in the left-hand column of the sequence chart in Fig. 3. This first step of actuation has the eiiect of closing switches SI, S2, S3, SI2, SI3, SIA, SII, SI'I and SIS, S20 and SZI. The closure of switches SI, S2 and S3 connects the motor armature MA to the propulsion bus. At the same time the motor held winding MF is prepared for energization by the closure of switches SI3 and SM in addition to closed switch SI2. Simultaneousn ly, the eld windings MGF and AGF of the exciter set EXC are connected through the closure of switches SI and SI'I' with the constant voltage bus CVB. Hence, now, the generators AG and MG are sufficiently excited to supply energizing current to the motor field MF and the alternator nelds. AGA and MGA are now seriesconnected through SI3 and SI12 to the eld circuits of the alternators ALI, ALB and ALS so that the excitation of the alternator eld windings AFI, AFE and AF3 is relatively high and the propulsion bus PB will consequently become energized. The motor iield winding MF is still disconnected due to the opening of switches SII! and SI I. The switches SI9, S20, and SZI effect a connection of the pilot motor PM to the propulsion bus PB so that now a speed responsive voltage is effective in coil CL of voltage regulator VRG. Switch SI8 being open in position +I, the voltage regulator is now operating and controls the energization of field winding AGF and hence the voltage of the alternator eld windings AFI, AF2 and AF3.

By now moving the control lever MCL into position +2, the above-mentioned switch-closure conditions remain unchanged with the exception that now switches SII) and SII are also closed (see Fig. 3). As a result, the eld winding MF of the propulsion motor MOT is connected to the exciter circuit EC and is energized from the exciter armature MGA, although in this stage the resistor R'I remains connected through switch SI 2 across the field winding MF.

By moving MCL a further step into position +3, the just-mentioned condition of the switching devices is changed by the opening of switch I2 and the closure of switch I8. The opening of switch SI2 has the effect of cutting the discharge resistor RII out of the motor eld circuit. The closure of switch SIS shunts the voltage regulator VRG out of the circuit of field winding AGF so that now the excitation supplied by the exciter bus EB to the alternator eld winding AFI is at its full value. It will be remembered that previous to the closure of switch SIS the eld of AFI was reduced in dependence upon the frequency of the propulsion current and hence on the speed of the engines. When lever MCL is in the position +3, the speed of the propulsion motor is close enough to synchronization to render the voltage control unnecessary.

When now moving MCL into the position denoted by +4 in Fig. 3, the previously existing switch condition is changed by opening switch SIS and closing SI5. As a result, the series connection of armatures AGA and MGA is interrupted, and the armatures are now so connected as to act independently of each other on the alternator and motor fields respectively. At the same time switches SIS, S20 and SZI are opened to disconnect the pilot regulator set PRS from the propulsion bus.

When nnally completing the motion of MCL by placing it into the run position denoted by +5 in Fig. 3, only switches SI, SZ, S3, SIU, SII, SI5 and SIS remain closed. Now the system is set for normal operating conditions. The propulsion speed is now dependent upon the adjustment of the motor speed lever SCL (Figs. 1 and 4) controlling the speed of the prime mover engines.

When moving the motor control lever MCL from run to stop, the reverse operation takes place. In order to reverse the direction of propulsion, lever MCL is moved from the stop position through the dynamic braking position B to the positions denoted consecutively by -I to +5 in the left-hand column of the sequence chart shown in Fig. 3. During the braking period, only switches S'I through SII are closed. As a result, the motor armature MA is disconnected from the propulsion bus PB and connected to the braking impedances R4, R5 and R6 and the motor field MF is energized and dynamic braking is obtained.

When moving lever MCL through positions -I through 5, an operation similar to the abovedescribed starting operation is performed with the exception that now switches SI, S2 and S3 remain open while switches S4, S5 and S6 are closed. This has the effect of reversing the direction of rotation of the propulsion motor MOT..

therwise, the starting sequence is identical with the one previously described.

As set forth in the foregoing description, the generator elds of the alternators are not energized at a time when their armature output circuits are connected to the propulsion bus. Consequently during this initial period or" operation the alternators will not be synchronized electrically but will run at approximately the same speed due to the action of the master speed control transmitter. When after this initial stage the propulsion motor is being started, its armature winding is connected to the propulsion bus, and the alternator fields are energized simultaneously. Due to their inherent time constant, the nelds will build up slowly, and power will be applied to the prime mover engines so gradually as to permit positioning of the governor fuel racks before the engine speed drops too low. The synchronization of the alternators will then occur as the elds build up. As a result, the sudden rush of power into the propulsion motor and the corresponding sudden application of load to the Diesel engines is avoided, thereby eliminating one of the component causes of the above-mentioned tendency to stall.

In order to improve this condition, by also reducing or eliminating the above-mentioned second component cause of the stalling effect, it is necessary in accordance with this invention to L reduce in periods of acceleration the alternator torque to a value which can be matched by the engines. The motor and alternator torque will be reduced if the alternator field current is reduced. This is apparent from the explanatory diagram shown in Fig. 5.

In Fig. 5, the ordinate indicates torque values in per cent of the normal torque, and the abcissa the related values of the propeller speed in per cent of normal revolutions per minute. The diagram refers to an operating stage at which the alternators run at 25% speed and are connected for astern operation. Two sets of curves denoted by A, A' and B, B', respectively, are illustrated. Curve A represents the engine torque required at normal alternator excitation and curve A' the motor torque also at normal eld excitation of the alternators. Curve B represents the engine torque required at reduced alternator excitation and curve B the motor torque at reduced alternator excitation. The normal excitation referred to by curves A and B is the magnitude of excitation required to synchronize the motor. The eX- citation, of course, must not be reduced to a point at which the torque requirement of the propeller exceeds the motor torque as this would result in stalling of the motor.

The method of control aimed at in accordance with this invention and approximated by the above described control system is to regulate the field current of the alternator eld windings so that the alternator torque remains at or near the maximum which can be developed by the engines without pulling the speed down below the minimum value required for stable operation. This is obtained by the action of the pilot regulator set PRS due to the fact that the control of the eld current supplied by the exciter bus EB is proportional to the engine speed, the regulator voltage produced by the armature GA being a measure of this speed. Consequently, the system according to the invention embodies, in fact, the objects and advantages stated earlier in this specifcation.

It remains to indicate suitable means by which 10 the above-described cooperative and sequential operation of the control switches is obtained. An embodiment of such means is illustrated in the diagram of Fig'. 6.

The system shown in Fig. 6 is identical, as to general setup and operation, with the embodiment described in the foregoing with reference to Figs'. l through 5. In distinction from Fig. 1, however", the illustration of Fig. 6 shows one of the three switching apparatus serving to connect the alternators to the propulsion bus, only one of these apparatus being represented in detail since the two others are designed and opera-tive in analogy thereto. Fig. 6 also contains a detailed showing of the switching apparatus for starting the motor.

The main elements of the system described in the foregoing will be recognized in Fig. 6 by their corresponding reference characters.

The circuit elements appertaining to alternator ALI are enclosed in Fig. 6 by a dash line denoted by DI. It is understood that the dash line enclosures D2 and D3 relating to the alternators ALZ -and AL3, respectively, represent a group of correlated elements similar to those enclosed by DI and described presently.

In order to control -the connection of alternator ALI to the propulsion bus PB in accordance with the foregoing description and with the sequence chart of Fig. 2, a number of contact fingers represented by circles and denoted by Al) through AI5 are arranged in proper relation to contact segments denoted by ID through I5 which are mounted on a slidable base ACA. The base is connected by a member AMI with the control lever CLI (see Fig. 4) and can be moved by means of this connection between an om start and run position identical with the same positions as indicated in Figs. '2 and 4. The designations of AIU through AIS applied in Fig. 6 t0 the contact ngers indicate that the respective contact fingers belong to the switch of the same designation shown in Fig. 1. When the contact base ACA (Fig. 6) is in the off position, only contacts AIS are closed by contact segment I5 in accordance with the oir position as indicated in the sequence chart of Fig. 2. In the start position of base ACA, contacts AIO, AI I, AI2 and AI5 are closed by means of the respective segments II), II, I2 and I5 which is also in accordance With the sequence chart of Fig. 2. In the run position, only switch A15 is open While the other pairs of contact fingers are bridged by the respective segments I0 through I4, as is also required by the chart of Fig. 2. Consequently, a switching device as just described is capable of performing the partly simultaneous and partly sequential actuation of the switches AIU through AIS.

The switching apparatus shown in Fig. 6 for obtaining thev sequence of switches SI through S2! according to the chart Fig. 3 comprises an arrangement of Contact fingers and a coordinated arrangement of contact segments carried by a segment base MCA which is conected by a member AM4 to the control lever MCL (Fig. 4) The contact ngers of the motor starting apparatus are represented in Fig. 6 by circles and are denoted by reference characters SI', S2', etc. serving to indicate their relation to the respective switch SI, S2, S3, etc. of Figs. 1 and 3. However, in order to simplify the switching apparatus and to reduce the number of contact ngers and Contact segments, several of the contact ringers and contact segments according to Fig. 6

arremete il serve to perform the function of several of the switches shown in Fig. l and denoted in the sequence chart in Fig, 3. For instance, the contact segments ItiI, IIl2 and |63 serve to bridge the pairs of contact ngers marked SI', S2 and S3', respectively, in the flve positions denoted by +I through +5. Another group of contact segments 2ll, 232, 263, 3M and 363 mounted on the segment base MCA are so connected and arranged that when the apparatus is Placed in any of the positions marked -I through -5 the polarity of the propulsion motor MOT and hence its direction of rotation is reversed. The segments 2.3i, 262, 233, and 303 also cooperate with the contact fingers denoted by Si', S2 and S3. Hence this finger and segment arrangement performs the function of the switches SI, S2, S3, S4, S5 and S6 according 'to Figs. 1 and 3. Similarly, the group of contact fingers denoted by the legend, SI2 to SES serves to perform the c.'-

functions of switches SI2 through Sl5 according to Figs. l and 3 in cooperation with corresponding contact segments denoted by III, IIE and ZI 5. rihe pair of Contact fingers S IB in Fig. 6, cooperating with segments Ill?, 2H) and 3io, correspond to switch Si@ in Figs. Vl and 3. The pairs of contact fingers SI 6 through S24 in Fig. 6 coo-perating with segments H6, 2i6, IIB, 2i8, H9, 2I9, I2E3,22l, l2I and 22I correspond as to their function to the switches Slis` -through S25 referred to in Figs. 1 and 3.

When actuating the motor starting lever MCL, the segment base MCA is displaced by the connecting member AMG so as to assume the positions indicated in Fig. 6 immediately above the segment base MCA in accordance with the positions indicated in the left-hand column of Fig. 3. When MCA is placed in any of these positions, the circuit connections established by the segments mounted on MCA correspond to those indicated in the sequence chart of Fig. 3. For instance, as will be seen from Fig. 6, when the segment MCA is placed in position +5 the contact pairs SI', S2', S3', SIB, SI-I and SI8 are bridged. This corresponds to the closure of the switches SI, S2, S3, Sid, SII, and ySIS indicated in Fig. 3 for position +5. Simultaneously, the two lower contact fingers of group .SI2 to SI5 are bridged by segment I I5 thereby closing the circuit of the exciter bus .EB in accordance with the closure of switch yI 5 indicated in the sequence chart. To mention another example, when the switching apparatus is positioned in accordance With lever position S (stop), the segment III closes the parallel connection of resistor Rl to motor field winding MFin accordance vwith the function of a closure of switch SI2 as indicated in Fig. 3. In this stop position, all other connections of the switching apparatus are open, which is also in conformity with the stop position S marked in the sequence chart.

The functional equivalence of the switching apparatus acco-rding to Fig. 6 with the requirements apparent from the sequence chart of Fig. 3 will be further apparent from another example. If the segment lbase MCA is in the position corre` sponding to B (dynamic braking), the braking resistors Rt, R5 and R6 are connected through segments 67, |68 and 99, respectively, with the leads connecting the motor arrangement to the propulsion bus PB. This corresponds to the closure of switches S'I, S8 and S9 as indicated for position B in the sequence chart of Fig. 3. At .the same timey the pairs of contacts Si@ and SII shown in Fig. 6 are bridged by segments 2 l@ 12 and Il I, respectively. This is in accordance with the closure of switches SIG and SII as shown in the sequence chart. All other connections are open also as required by the sequence chart.

It will likewise be seen that in all other positions of ythe switching apparatus for starting the motor, the showing of Fig. 6 is in accordance with the requirements of the invention as explained previously.

Since the levers CLI, CL2 and CL3 (see Fig. l4t) are to be operated so that at least one of them is in the run position before the motor starting lever MCL is moved out of its stop position, a suitable interlock may be provided if desired.

The interlocking can be eifected mechanically by a latch mechanism or by electrical means performing a similar function. For instance, a magnetic locking device may be provided for blocking lever MCL in the illustrated stop position, and an electric limit switch may be arranged for each of levers CLE, CL2 andCLS so as to be closed when the respective lever CLI, CL2 or CL3. is placed in the run position. lf these limit switches are connected in parallel to the coil for unlocking the magnetic device, the starting lever MCL can be moved only if at least one of levers CLI, CL2 and CL3 is positioned for a proper energization of the propulsion bus. The justmentioned possibility .of providing interlocks is not illustrated in the drawing because various forms of suitable interlocks are well known in the art and because the presence and particular design of such an interlock is not an essential feature of the invention proper. It will be understood from the foregoing that the control system will operate properly, if no interlock is provided, although more attention is then required from the operator.

Since various changes in our invention may be '..i made without departing from the spirit and scope thereof, it is intended that all matters contained in the foregoing description and shown in the accompanying drawings shall vbe interpreted as lustratve and not in a limiting sense.

We claim as our invention:

l. An electric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a field circuit, an alternating current propulsion motor, a propulsion bus for feeding current from said generators to said propulsion motor, a pilot regulator set having a pilot motor connected to said bus and a pilot generator actuated by said pilot motor to Yprovide a voltage in accordance with the frequency of the current in said bus, voltage-responsive control means having an actuating member connected to said pilot generator and a variable impedance member controlled by said actuating member to vary its effective impedance value in dependence upon said voltage, said impedance member being connected with said field circuits for providing low excitation at low frequency `and higher excitation at higher frequency of said current.

2. An electric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a circuit for providing eld excitation. contact means connected with said circuits for controlling said excitation, a propulsion bus., a plurality of switch means arranged between said propulsion bus and each of said armatures respectively for connecting the latter to said bus, propulsion motor, switch means for connecting said motor to said bus, said switch means and said contact means being connected with one another to prevent said excitation from becoming effective before said propulsion motor is connected to said bus, a pilot regulator set having a motor connected to said bus and a pilot generator actuated by said motor to provide a pilot voltage in accordance with the frequency of the current in said bus, voltage-responsive control means having an actuating member connected to said pilot generator and a variable impedance member controlled by said actuating member to vary its effective impedance value in dependence upon said pilot voltage, said impedance member being connected with said circuits for providing low excitation at low frequency and higher excitation at higher frequency of said current.

3. An electric ship propulsion system cornprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a eld circuit for providing excitation, contact means connected with said eld circuits for .controlling said excitation, a propulsion bus, switch means arranged between said propulsion bus and each of said armatures respectively for connecting the latter to said bus, a propulsion motor, switch means for connecting said motor to said bus, said switch means and said contact means being connected with one another to prevent said excitation from becoming effective before said motor is connected to said bus, and control means responsive to the motor speed and connected to said eld circuits for controlling the latter to reduce said excitation and in dependence on reduced motor speeds.

4. An electric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchnonism, each of said sets having a generator including an armature and a field circuit for providing excitation, an exciter set including a constant speed motor and an exciter generator with an exciter armature and a field winding, said exciter armature being mechanically connected with said constant speed motor to be driven thereby so that the output voltage of said exciter generator is in accordance with the energization of said iield winding, controllable circuit means connected to said exciter field winding for supplying variable energization thereto, a propulsion bus, connecting contactors arranged between said propulsion bus and said armatures respectively, a propulsion motor, switch means for connecting said motor to said bus, said switch means, contactors and controllable circuit means being interlinked so as to provide substantially zero excitation in said field circuit before said motor is connected to said bus and normal excitation when said motor runs substantially at full speed.

5. An electric ship propulsion system comp-rising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronisrn, each of said sets having a generator including an armature and a field circuit for providing excitation, an exciter set including a constant speed motor and an exciter generator with an exciter armature and a field winding, said exciter armature being mechanically connected with said constant speed motor to be driven thereby so that the output voltage of said exciter generator is in accordance with the energization of said field winding, a control circuit connected to said exciter field winding for supplying energization to the latter and containing contact means for controlling said energization, a propulsion bus, switch means arranged between said propulsion bus and said armatures respectively, a synchronous propulsion motor, switch means for connecting said motor to said bus, all of said switch means and said contact means being interconnected so as to apply said generator excitation only when said motor is connected to said bus.

6. An electric ship propulsion system comprising in combination prime movers, generators each being mechanically connected with one of said prime movers respectively to be driven thereby, a propulsion bus connected with said generators. a propulsion motor, a switching device for connecting said motor to said bus, said generators having circuit means for providing them with' eld excitation, and switch means disposed in said circuit means and connected with said switching device to be operated in dependence upon the latter so that said iield excitation is applied when said motor is connected to said 7. An electric ship propulsion system comprising in combination prime movers having a master speed control so as to run at approximately the same speed, generators each being mechanically connected with one of said prime movers respectively to be driven thereby, each of said generators having circuit means for providing it with field excitation, a propulsion bus electrically connected to said armatures, a propulsion motor, and switch means having contacts for connecting said motor to said bus and said circuit means to said generator so as to prevent said excitation from becoming effective before connecting said motor.

8. An electric ship propulsion system comprising in combination prime movers, generators each having an armature connected with one of said prime movers respectively to be driven thereby, a propulsion bus connected with said generators, a propulsion motor, a switching device for connecting said motor to said bus, said generators having circuit means for providing them with eld excitation, control means forming parts of said circuits means fiorvarying said excitation, and sequentially operating switch means associated with said circuit means and said control means and connected with said switching device for controlling said energization in dependence upon the operation of said switch device so as to prevent said excitation before said mlotor is connected to said bus and varying said excitation when said device is adjusted from a starting position towards full operation position.

9. An electric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a eld circuit for providing iield excitation, regulating means connected with said eld circuit for controlling said excitation, a propulsion bus, switch means arranged between said propulsion bus and each of said armatures, a synchronous propulsion motor, connecting means for attaching said motor to said bus', said switch means, connecting means and regulating means being operatively connected with one another so as to provide substantially zero excitation in said held circuit before said motor is connected to said bus, regulated excitation when starting said motor, and normal excitation at synchronization of said motor.

1Q.An electric ship propulsion system com.- pri-sing in combination prime-mover generator setshaving a master speed control tending to operate Said sets in approximate synchronism, each of said sets having a generator including an armature and a eld circuit for providing eld excitation, an energizing voltage source connected with said eld circuits, regulating means for varying the voltage of said source, contact means. connected with said regulating means for QQntrQllng the latter, a synchronous propulsion motor, circuit means disposed for connecting said IIlQtQl? t0. the armature ofv said generators and incl 'ng a connecting and disconnecting switch, said switch and said contact means being con- IleCted. with oney another for causing said contact means to control said regulating means in dependence upon the operation of said switch so as to suppress said generator field excitation when said motor is disconnected and increase said; excitation from low to. normal when said motor is connected to said bus and increases its speed to approximate synchronism.

il. A nelectric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a. generator including an armature and a eld circuit for providing field excitation, regulating means connected with said eld circuit for varying said excitation, a propulsion bus, switch means for connecting said propulsion bus with said armatures respectively, a synchronous propulsion motor, switch means. for connectingV said motor t-o said bus, sai-d switch means and said regulating meansbeingconnected with one another to prevent said excita tion from becoming effective before connecting said motor to said bus, control means responsive to the. prime-moverspeed and connected to said regulating means for controlling the latterto reduce said excitation at reduced prime-mover speeds andy in dependence thereon.

12; An; electricship propulsion system comprising in combi-nation prime movers, generators each having an armature connected with one of said prime movers respectively tol be driven thereby; a propulsion bus connected with said generator, a propu-lsicn motor, a. switching device for connecting said motor to said bus, said generators having circuit means for providing them with eldexcitation, switch means disposedinsaid circuit means and connected with sai-d switching device to be operated in depend.- enceupon the operation of the latter so that said field excitation is applied when said motor is. connected to said bus, and control means responsive to the motor speed and connected to sai-d circuit means for controlling said field excitation soas to reduce said excitation at reducedA primemover speeds.

13.-. An. electric ship propulsion system comprising in combination a prime mover, an altermating-current generator having an armature connected with said pri-me mover, a propulsionbus connected with said generator, a synchronousmotor connected to said bus, said generator having circuit means. forproviding it with field excitations. a regulator set having an alternatingcurrent motor connected to said bus and a directe current pilot generator actuated by said latter motor to provide a pilot voltage in accordance with the frequency of the current in said bus, said pilot generator being connected with said circuit means for varying said field excitation ofv said alternating-current generator so as to provide low excitation at low frequency and higher excitation at higher frequency of said current 14. An electric ship propulsion system comprising in combination prime-mover generator sets having a master speed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a iield circuit for providing field excitation, an exciter set including a constant speed motor and an exciter generator with an exciter armature and a eld Winding, said exciter armature being mechanically connected with said constant speed motor to be driven thereby so that the output voltage of said exciter armature is in accordance with the energizetion of said field winding, controllable circuit means connected to said exciter eld winding for supplying variable energization thereto, a propulsion bus, a propulsion motor connected to said bus, frequency-responsivc control means connected to said controllable circuit means for regulating the latter in accordance with the speed of said prime-mover generator in order to lower with said constant speed motor to be driven.-

thereby so that the output voltage; of said ex citer generator is in accordance with the energization of said eld winding, a eld` control cir-..

c-uitconnected to said exciter eld winding for suppl-ying energization to the latter and con,- taining contact means for controlling said ener;- gization, a propulsion bus, selective switch meansfor connecting said respective armatures with. said propulsion bus, a synchronous propulsion motor, switch means for connecting said motorA to said bus, said dine-rent switch means: and said Contact means being interconnected to operate, in dependence upon one another for applying said generator el'dA excitation only when said.

propulsion motor is connected to said bus, a pilot, regulator set having a motor connected to said. bus and a pilot generator actuated by said motor to provide a pilot voltage in accordance with the frequency of the current in said bus, voltage-ra sponsive control means having an actuatingmember connected to said. pilot generator and a variable impedance mem-ber controlled. by said actuatingrnember to vary itseiective impedancevalue in depend-ence upon said. pilot voltage, said impedance member being connected between said contact means and: sa-id exciter eld winding forv varying said energization of said; winding and: thereby said generator field excitation so ast to provide low excitation at l'ow frequency and higher excitation at higher frequency of. said current..

angers i6. An electric ship propulsion system com'` prising in combination prime-mover generator sets having a master spe ed control tending to operate said sets in approximate synchronism, each of said sets having a generator including an armature and a iield circuit for providing field excitation, an exciter set including a constant speed motor and an exciter generator with an exciter armature and a eld winding, said exciter armature being mechanically connected with said constant speed motor so that the output voltage of said exciter set is in accordance with the energization of said field winding, a control circuit connected to said exciter field winding for supplying energization to the latter and containing contact means for controlling said energization, a propulsion bus, selective switch means for connecting said respective generator armatures with said bus, a synchronous propulsion motor, switch means for connecting said motor to said bus, said different switch means and said contact means being interconnected to operate in dependence upon one another for applying said generator field excitation only when said motor is connected to said bus, a pilot regulator set having a motor connected to said bus and a pilot generator actuated by said motor to provide a voltage in accordance with the frequency of the current in said bus, voltage-responsive control means having an actuating member connected to said pilot generator and a variable impedance member controlled -by said actuating means to vary its effective impedance value in dependence upon said voltage, said impedance mem-ber being connected between said contact means and said exciter iield winding for varying said energization of said winding and thereby said generator field excitation so as to provide' low excitation at low frequency and higher excitation at higher frequency of said current, and a contactor for rendering the pilot regulator set ineffective at high speeds of said propulsion motor, said contactor being connected with said interconnected switch and Contact means for operating in a given sequence thereto in order to be actuated during the starting control stage of said propulsion motor.

17. An electric control system comprising in combination a plurality of prime movers having speed regulating means and a common master control for operating at substantially the same speed, a corresponding number of alternators each being mechanically connected with one of said prime movers respectively to produce a voltage frequency determined by said speed regulating means, a bus, switch means for electrically connecting said individual armatures to said bus, a synchronous drive motor having a motor armature and afield winding, a switching device for electrically connecting said motor armature to said bus in order to run said motor at a speed corresponding to said regulata-ble frequency, said alternators having field windings respectively for providing them with excitation, direct current supply means connected with said alternator and motor eld windings, a plurality of contact means interposed between said current supply means and said respective eld windings to control the energization of said windings by said current supply means, circuit control means associated with said direct current supply means for varying said energization of said windings, said circuit control means including further contact means for effecting said variation, said switching device and said contact means being mechanically integrated to form a sequentially operating contact apparatus having for each of said alternators av single actuating member for controlling the connection to said -bus and the eld energization of said drive motor as well as the energization of said alternator so that. when actuating said member, said field windings are energized when said motor armature is connected to said bus, whereafter upon further actuation of said member said field energization is varied so as to increase at increasing frequency and motor speed.

18. An electric control system comprising in combination a plurality of prime movers having speed regulating means and a common master control for operating at substantially the same speed, a corresponding number of alternators each being mechanically connected with one of said prime movers respectively to produce a voltage frequency determined by said speed regulating means, a bus, switch means for electrically connecting said individual armatures to said bus, a synchronous drive motor having a motor armature and a field winding, a switching device for electrically connecting said motor armature to said `bus in order to run said motor at a speed corresponding to said regulatable frequency, said alternators having eld windings respectively for providing them with excitation, direct current supply means connected with said alternator and motor field windings, a plurality of contact means interposed between said current supply means and said respective field windings to control the energization of said windings, said switching device and said contact means being operatively connected with one another and having for each of said alternators a Icommon movable actuating member for controlling the energization and connection to said ibus of said drive motor as well as the field energization of said appertaining alternator so that by actuating said movable member said field windings of said motor and said alternator are energized when said motor armature is connected to said bus, and frequencyresponsive control means having an input circuit electrically connected to said bus and an output circuit connected to said direct current supply means for reducing the energization of said alternator field windings by said current supply means at low values of said frequency.

19. An electric control system comprising in combination a plurality of prime movers having speed regulating means and a common master control for operating at substantially the same speed, a corresponding number of alternators each having an armature connected with one of said prime movers respectively to produce a voltage frequency determined by said speed regulating means, a bus, switch means for electrically connecting said individual armatures to said bus, a synchronous drive motor having a motor armature and a field winding, a switching device for electrically connecting said motor armature to said bus, said alternators having field windings respectively for providing them with excitation, direct current supply means connected with said alternator and motor field windings, a plurality of contact means interposed between said current supply means and said respective field windings to control the energization of said windings, said switching device and said contact means being operatively connected to one another and having for each of said alternators a common movable actuating member :for controlling the energization and connection to said bus of said drive motor as well as the field energization of said appertaining alternator so that by actuate aprire-564s ing said member said eld" windings of isa-id nio.- tor and'saidlatteralternator are energized when said4 motor armature isI connected to said'v bus. frequency-responsive control means having an input circuitA electrically connected? tov said bus and anoutput` circuit connected to said direct current supply meansl for reducing the energization oisaid alternator field' windings by said currentsupply means at lowf valuesof said frequency, and a contacterconnected with said frequency-responsive control means, saidcontact'or being' also' connectedwith. said` switching device and said contact means to be controlled by' saidmovable member upon: further' actuation of` the latter in' order to render said trequencyn responsive control means@ ineffective in a late stage of the starting operation ofsaid drilve motoriV 20; An electric snip propulsion system com-y prising an alternating-ecurrent. generator having4 20 for causing said voltage to vary.' in*` accordance with variations of said frequency, and circuit means connecting saidl regulatingl means with saideld Winding for regulating the ield excita.- ticn oi said generator under control by said voltage.

21. An electric ship propulsion system, comprising an alternating-current generator having.

a field winding, a speed-adjustable prime mover connected t'o said generator for operating thelatter to provide alternating current Whose fre.-

quency depends upon they speed ot said prime.

cordance with said frequency', and circuitmeans.

connecting said pilot generator with said field Winding for regulating the eld excitation of said alternating-current generator so. as to re-` duce and increase said excitation with a dropland increase,respectively, of said prime mover speed..

ERLING FRISCH.. MARION R. LORY. 

